1. Field of the Invention
The present invention relates to damper devices used for electronic apparatuses such as mobile phones and personal computers.
2. Background Art
With electronic apparatuses such as mobile phones and personal computers becoming increasingly smaller and lighter, many products are adopting designs that attach a movable housing to a stationary housing in an openable and closable manner, a so-called folding design. In response to this trend, hinge devices and damper devices used in these electronic apparatuses are also required to ensure reliable and diverse opening and closing operations.
A conventional damper device is described next with reference to FIGS. 5 to 7.
FIG. 6 is a sectional view and FIG. 7 is an exploded perspective view of the conventional damper device. In these drawings, protrusion 2A projecting outward is formed on a periphery of each of multiple disk-like stationary plates 2 made of metal. Stationary plates 2 are housed in stationary case 1 in a movable manner in an axial direction by inserting this protrusion 2A into groove 1A in substantially cylindrical stationary case 1 made of metal. This axis is a central axis of substantially-cylindrical stationary case 1. Stationary plates 2 do not rotate relative to stationary case 1 when movable shaft 3 rotates, which is described later, by the presence of protrusion 2A.
Multiple disk-like movable plates 4 made of metal are alternately sandwiched between stationary plates 2, and square hole 4A is created at the center of each of movable plates 4. Substantially prismatic movable shaft 3 made of metal, inserted into stationary case 1, passes through this square hole 4A, and thus movable plates 4 are attached to movable shaft 3 in a movable manner in an axial direction. Movable plates 4 rotate in response to the rotation of movable shaft 3 by inserting substantially prismatic movable shaft 3 through square hole 4A of each movable plate 4.
Coiled spring 6 is set between the right side face (the right side in FIG. 6, hereinafter) of cover 5, which covers an opening in the left end face (the left side in FIG. 6, hereinafter) of stationary case 1, and stationary plate 2 in a slightly compressed state. In this way, stationary plates 2 and movable plates 4 contact in resilient manner. A high-viscosity lubricant (not illustrated) is applied between stationary plates 2 and movable plates 4.
Ring-like O-ring 7, typically made of rubber, is set between cover 5 and movable shaft 3 in a slightly but entirely compressed state by stopper ring 9, and ring-like O-ring 8, typically made of rubber, is set between cover 5 and stationary case 1 so as to hermetically seal the interior of stationary case 1.
The right end of movable shaft 3, to which movable plates 4 and stationary plates 2 are attached, is rotatably held by the inner side face of stationary case 1. Attachment part 3A formed at the left end of movable shaft 3 rotatably protrudes from the left side face of cover 5. This configures damper device 10.
Damper device 10 as configured above is installed in a mobile phone, for example, shown in a perspective view in FIG. 5. More specifically, stationary case 1 is fixed to stationary housing 11 where control panel 11A such as keys and sound input part 11B such as a microphone are formed on its top face. Attachment part 3A of movable shaft 3 is fixed to movable housing 12 where display 12A such as LCD and sound output part 12B such as a speaker are formed on its surface.
Hinge device 13 configured with components including multiple cams (not illustrated) and spring (not illustrated) is mounted between stationary housing 11 and movable housing 12. An electronic apparatus is configured such that this hinge device 13 applies a force to movable housing 12 in a closing direction and opening direction relative to stationary housing 11.
In the above structure, when a button (not illustrated), for example, on the side face of stationary housing 11 is pushed for operation while movable housing 12 is closed, the cams, spring, and so on of hinge device 13 act to apply a force in the opening direction to movable housing 12. Accordingly, movable housing 12 starts to open.
Then, movable shaft 3 whose attachment part 3A is fixed to movable housing 12 rotates in the opening direction, and movable plates 4 attached to movable shaft 3 rotate. Stationary plates 2, which are alternately disposed between movable plates 4 and attached to stationary case 1, resiliently contact these movable plates 4 due to the action of spring 6. In addition, a high-viscosity lubricant is applied between movable plates 4 and stationary plates 2. Accordingly, a resistance force (damping force) against the opening direction is generated between movable plates 4 and stationary plates 2.
In other words, hinge device 13 applies the force in the opening direction to movable housing 12, but damper device 10 applies the resistance force against the opening direction at the same time. Accordingly, movable housing 12 opens gradually instead of suddenly.
In general, the force of hinge device 13 to open movable housing 12 is the greatest immediately after movable housing 12 starts to open, and this force becomes smaller as an opening angle becomes wider. On the other hand, the resistance force of damper device 10, i.e., the damping force, is constant, regardless of the opening angle, because this force is the resistance force generated between disk-like movable plates 4 and stationary plates 2 which resiliently contact via the lubricant.
In other words, damper device 10 applies a constant resistance force to movable housing 12 so as to gradually open movable housing 12, and thus the opening speed is determined by the force of hinge device 13 to open movable housing 12.
Accordingly, movable housing 12 opens fast immediately after the operation, and then the opening speed slows as the opening angle becomes wider.
One known prior art is Japanese Patent Unexamined Publication No. 2004-150575.
In the conventional damper device, however, only a constant damping force can be obtained because the damping force is the resistance force generated between disk-like movable plates 4 and stationary plates 2 which contact resiliently via the lubricant. The opening speed of movable housing 12 is thus determined by the force of hinge device 13 to open movable housing 12. Accordingly, the conventional damper device cannot be applied to diverse opening and closing operations, such as to open movable housing 12 at a constant speed from immediately after starting to open until movable housing 12 opens to a predetermined angle.